PROJECT SUMMARY/ABSTRACT Over 5 million people in the US received treatment in 2014 for substance use disorders (SUDs), which are chronic illnesses that require ongoing care and carry significant risk of relapse. Relationship processes may play a powerful role in the recovery trajectories of people with SUDs, with stigma acting as a barrier to and social support acting as a facilitator of reduced substance use, treatment retention, and medication adherence. Disclosure of SUDs represents a gateway to stigma and social support from others. Interventions that help people in recovery decide to whom, why, when, what, and how to tell others about their SUD recovery status may help them disclose in ways that minimize risk of stigma and maximize access to social support from others, thereby supporting their recovery efforts. The goal of the proposed Mentorship Research Scientist Development Award (K01) is to facilitate my growth into an independent investigator who studies and intervenes in relationship processes among people in recovery from SUDs, ultimately promoting long-term recovery among this population. To achieve this goal, I will pursue a training plan to build expertise in SUDs, develop mastery in social network research, and gain training in intervention science. This training plan draws on a wealth of institutional resources at Harvard Medical School, Boston Children's Hospital, Massachusetts General Hospital, and the Harvard Clinical and Translational Science Center, and consists of mentorship from experts; formal training via courses, workshops, and programs; attendance at national meetings; and career development activities. I will apply my training to a research project that aims to: (1) examine longitudinal associations between disclosure, stigma, social support, and SUD recovery-related outcomes among people receiving SUD treatment; (2) develop an intervention to help people disclose SUD recovery to others in ways that minimize risk of stigma and maximize access to social support; and (3) pilot the disclosure intervention among people receiving treatment for SUDs to evaluate its acceptability and feasibility. These aims will be reached by conducting a longitudinal egocentric social network study with 160 people receiving treatment for SUDs (150 for study + 10 for pilot); online focus groups with 15-20 people receiving treatment for SUDs, providers of SUD treatment, and friends and family of people receiving treatment for SUDs; and a mixed- methods pilot study of the intervention with 50 people receiving treatment for SUDs. All work will be conducted in Boston, Massachusetts, which is currently experiencing an opioid crisis. Results of the study will form the foundation an NIH R01 application to evaluate the disclosure intervention in the context of a large-scale randomized control trial. This will ensure my transition into an independent investigator and contribute to the long-term recovery efforts of people receiving treatment for SUDs.